The MP 18.1 manufactured by Theodor BergmannAbteilung Waffenbau was the first practical submachine gun used in combat. It was introduced into service in 1918 by the German Army during World War I as the primary weapon of the Sturmtruppen, assault groups specialized in trench combat. Although MP18 production ended in the 1920s, its design formed the basis of most submachine guns manufactured between 1920 and 1960.

The firepower of this new class of weapons made such an impression on the Allies that the Treaty of Versailles specifically banned further study and manufacture of such light automatic firearms by Germany.[1]

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What became known as the "submachine guns" had its genesis in the early 20th Century and developed around the concepts of infiltration and fire and movement, specifically for the task of clearing trenches of enemy soldiers, an environment within which engagements were unlikely to occur beyond a range of a few feet.

In 1915, the German Rifle Testing Commission at Spandau decided to develop a new weapon for trench warfare. An attempt to modify existing semi-automatic pistols, specifically the Luger and C96 Mauser failed, as accurate aimed fire in full automatic mode was impossible due to their light weight and high rate of fire of 1,200 rounds per minute. The Commission determined that a completely new kind of weapon was needed. Hugo Schmeisser, working for the Bergmann Waffenfabrik was part of a team composed of Theodor Bergmann and a few other technicians. They designed a new type of weapon to fulfill the requirements, which was designated the Maschinenpistole 18/I. It is not clear what the "I" designation is intended to indicate, although its successor, the MP28, was designated the Maschinenpistole 28/II.

Full-scale production did not begin until early 1918.[2] Though technically not the world's first submachine gun, being beaten by the double-barreled Italian Villar-Perosa of 1915, in modern usage of the term the MP 18 is considered the world's first submachine gun since the Villar Perosa had been designed to be used as a light machine gun on aircraft before it was adapted to infantry use as a single-barreled shoulder-fired weapon in late 1918.

The MP 18 primarily served in final stages of World War I in 1918, especially in the so-called Kaiserschlacht offensive. At least 5,000 MP 18.1s were built and used during World War I, based upon observed serial number ranges of captured weapons; however, it is possible that up to 10,000 were built for the war. Though production was outlawed by the Treaty of Versailles, manufacture continued in secret into the early 1920s, as the final production total (again, based upon observed serial numbers) ended at around 35,000.

The MP 18 proved to be an excellent weapon. Its concept was well-proven in trench fighting. The basic design directly influenced later submachine gun designs and showed its superiority over the regular infantry rifle in urban, mobile, and guerrilla warfare. The MP 18 served with German police and paramilitary forces after the end of the war. It was widely used in combat by the Freikorps Von Epp against the Spartacus League in Bavaria and by other Freikorps in Berlin, where its efficiency in urban combat was demonstrated. Since the Treaty of Versailles prohibited the use and manufacture of pistols with a barrel over four inches (102 mm) and/or a magazine capacity over eight rounds, all Trommel Magazines TM 08 were destroyed.

Since the treaty allowed the Weimar Republic to keep a small quantity of submachine guns for police use, a few hundred MP 18.1s were modified to accept Schmeisser's original 20-round magazine design. This modification, conducted by Haenel Waffenfabrik, required removal of the existing magazine well collar, and replacement with a different one. These weapons were overstamped with the date "1920" on the receiver and magazine well to show they were legitimate weapons owned by the Weimar Republic and not war bringbacks or clandestine weapons.

Bergmann sold the license of the MP 18. 1 to SIGSwitzerland; the Swiss made model was known as SIG Bergmann 1920. It existed in .30 Luger, 9mm Parabellum and 7.63 mm Mauser. The Bergmann MP 18.1 represents a milestone both in terms of armament technology and warfare tactics. It opened the way for a whole new class of weapons and triggered the research for lighter automatic firearms to be used by mobile troops. Its first direct competitors did not see service in World War I, but most of them saw use in all the limited conflicts taking place in the inter-war period.

The Chinese produced a modified MP 18 in Tsing Tao with the assistance of Heinrich Vollmer. The French, despite being moderately interested by this class of armament because they had designed and introduced in service many semi-automatic and automatic weapons, immediately launched studies based on captured MP 18s. The design of the STA 1922 was adopted and the MAS 1924[3] entered service and was used in colonial war. The French MAS 35 and MAS 38 derived from one of the many prototypes of the immediate post war.

The Austrian Steyr MP 34 was created by a team of technicians led by Louis Stange who designed a submachine gun for Rheinmetall in 1919 and used Bergmann's MG 15 to design the MG 30. The SIG Bergmann 1920 was used by Finland and Estonia, it was the inspiration for the Estonian Tallinn 1923 and the Finnish Suomi model 31, which in turn inspired Degtyarev for his PPD 34.

Emil Bergmann, Theodor Bergmann's son designed the MP 32 that evolved into the MP34 as adopted by Denmark before to receive the MP35 name when adopted by nascent Wehrmacht in 1935. This submachine gun is often mistaken with the Mitraillette 34, a MP28 made in Belgium by Pieper Bayard, former Bergmann licensed manufacturer or with the MP34 made by Steyr. It is easy to identify the Bergmann MP 32/34/35 or its final version 35/1 since the cocking lever works exactly like a rifle bolt.

In 1940, with a pressing need for individual automatic weapons, the British copied the MP 28 and developed the Lanchester submachine gun for the Royal Navy. Solidly built with the use of brass for the magazine well, and a bayonet mount, it entered service in 1940. The magazine and the bolt of the MP 28 could be used in the Lanchester.

A soundly engineered piece of equipment with near commercial grade fittings and finish, the MP 18 was a heavy weapon, weighing over 5 kg (11.0 lb) when fully loaded. The receiver tube was very thick (~3 mm), compared with later World War II submachine guns with half that thickness or less, such as the Sten gun or MP 40.

Berlin 1919

Though Schmeisser designed a conventional 20-round-capacity "box" magazine for the weapon, the Testing Commission, for practical reasons, insisted that the MP 18 be adapted to use the 32-round TM 08 Luger "snail" drum magazine that was widely used with the long-barreled version of the P 08 pistol known as the Artillery model.

Like many other open-bolt designs, the MP 18 was prone to accidental discharge. If the buttstock of a loaded gun was given a hard knock while the bolt was fully forward, the gun could accidentally fire because of the bolt overcoming the action spring resistance and moving rearward enough to pick up a round, chamber it and fire. Soldiers liked to leave the bolt of their firearm in this closed or forward position, so dirt and debris would not enter the barrel and chamber. This 'Bolt-closure' practice acted as a dust cover for the weapon's chamber, preventing a malfunction from occurring because of the presence of foreign debris, but making accidental discharge more likely.

The German police asked for an external safety on their MP 18s, and a universal bolt-locking safety was added on all the submachine guns used by the police. Later submachine gun designs like the Sten and the MP 40 were modified to allow the cocking handle to be pushed inwards to lock the closed bolt to the tubular receiver casing. This design change prevented accidental discharges when the bolt was left forward and a loaded magazine was inserted.

The original MP 18.1 was designed to use the snail drum magazine of the Luger Artillery model pistol. This rotary design type of magazine holds 32 rounds of 9 mm Parabellum, the user having to load the magazine with a proprietary loading tool. A special sleeve was required when the snail drum was used on the MP18 to stop the snail drum from being inserted too far in the magazine well.

After 1920, the MP 18 was modified to use a straight magazine similar to those used in the later developed MP 40 submachine gun. The MP18 could only fire in the fully automatic mode. Its successor, the MP 28/2, received a modified mechanism with a selector for single shot or fully automatic fire.

Britain directly copied the MP28 at the beginning of World War II. The result was the Lanchester submachine gun, which saw service with the Royal Navy. The British Sten used the side-mounted magazine configuration and a simplified version of the open bolt firing operating system of the MP28.

The Soviet Union made a similar use of MP 18 design in their PPD-40 sub machine gun in 1934. Further development of the PPD-40 led to the simplified and mass-produced PPSh-41.